A Christmas Crease is found on summer clothing when you grab them out of the closet/draw in the New Year. This permanent looking crease is embedded in the clothing because they've been stored in the same spot for a period of time.

Bob shows up at work on a spring Monday morning with ruler-straight line across his chest on his shirt:

Co-Worker: "Hey Bob, nice shirt. Were you trying to impale yourself on the end of a table or something?"

Bob: "Thanks, Dick. No, it's just last seasons shirt with a Christmas Crease from the holidays"